Primitive islets contain two populations of cells with differing glucagon immunoreactivity

Area of Science:

• Endocrinology
• Cell Biology
• Histology

Background:

• Pancreatic islets house endocrine cells producing hormones like insulin, glucagon, and somatostatin.
• Glucagon's structure and cellular localization are crucial for understanding glucose homeostasis.
• Variations in hormone immunoreactivity can indicate different cellular processing or cell types.

Purpose of the Study:

• To characterize the different types of glucagon-producing cells in ratfish pancreatic islets.
• To investigate the accessibility of C-terminal and N-terminal glucagon epitopes in various cell types.
• To explore the presence and characteristics of glucagon-immunoreactive cells in pancreatic ducts and gastrointestinal mucosa.

Main Methods:

• Immunofluorescence staining using specific antisera against insulin, glucagon (N-terminal and C-terminal), and somatostatin.
• Proteolytic treatment of tissue sections to assess epitope accessibility.
• Microscopic examination of pancreatic islets, ducts, and gastrointestinal mucosa.

Main Results:

• Ratfish pancreatic islets exhibit diverse glucagon-immunoreactive cell populations.
• One cell type reacted with both N-terminal and C-terminal anti-glucagon sera.
• Another cell type, initially reactive only to N-terminal anti-glucagon, became C-terminal reactive after proteolytic treatment, suggesting a masked epitope.

Conclusions:

• The study identifies distinct glucagon-producing cell subtypes within the ratfish pancreas.
• A subset of pancreatic and gastrointestinal cells possess a masked C-terminal glucagon sequence, unmasked by proteolysis.
• These findings highlight differential processing and presentation of glucagon in various cell types and locations.